Resin impregnation method, method of manufacturing wavelength-conversion module, and wavelength-conversion module

ABSTRACT

A method of impregnating voids of a sintered metal body having a porous structure with resin, the method comprising preparing a resin material that contains a defoamer containing hydrophilic or hydrophobic particles, defoaming the prepared resin material by reducing pressure of the resin material, applying the defoamed resin material onto a surface of the sintered metal body, impregnating the voids with the resin material by reducing pressure of the sintered metal body and the resin material applied to the surface of the sintered metal body so as to expel gas from the voids; and curing the resin material by heating.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2020-072941, filed on Apr. 15, 2020, the contents of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a resin impregnation method, a methodof manufacturing a wavelength conversion module, and a wavelengthconversion module.

Description of the Related Art

In recent years, high-output light sources that convert the wavelengthof blue light from semiconductor lasers by using phosphors have beenwidely used as light sources for headlamps, various illuminationdevices, laser projectors, and the like. The phosphor in such a lightsource generates heat along with the conversion of wavelength, whichrequires the light source to efficiently release the heat generated fromthe phosphor. In particular, wavelength-conversion devices employed inlight sources using semiconductor lasers are required to usewavelength-conversion members with excellent durability and toefficiently release heat generated from the wavelength-conversionmembers.

In order to meet these requirements, Japanese Patent Publication No.2019-207761 discloses a wavelength-conversion device (also called awavelength-conversion module) that uses a ceramic phosphor as awavelength-conversion member and joins the ceramic phosphor to a heatdissipation member using a joining portion having a sintered structure.According to JP 2019-207761 A, high thermal conductivity can be obtainedby using the joining portion having the sintered structure that containsat least one of silver, gold, or copper.

SUMMARY OF THE INVENTION

However, there have been growing demands for light sources with higheroutput and also wavelength-conversion modules with higher reliabilitythat are suitable for use in the light source and includewavelength-conversion members.

An object of the present disclosure is to provide a resin impregnationmethod that enables manufacture of a wavelength-conversion module withhigh reliability.

Another object of the present disclosure is to provide awavelength-conversion module with high reliability and a method ofmanufacturing the wavelength-conversion module.

A resin impregnation method according to the present disclosure is amethod of impregnating voids of a sintered metal body having a porousstructure with resin, the method including: preparing a resin materialthat contains a defoamer containing hydrophilic or hydrophobicparticles; defoaming the prepared resin material by reducing pressure ofthe resin material; applying the defoamed resin material onto a surfaceof the sintered metal body; impregnating the voids with the resinmaterial by reducing pressure of the sintered metal body and the resinmaterial applied to the surface of the sintered metal body so as toexpel gas from the voids; and curing the resin material by heating.

A method of manufacturing a wavelength-conversion module according tothe present disclosure comprises joining a wavelength-conversion memberonto a base using a joining member, the method including: preparing ametal paste containing metal powder and applying the metal paste ontothe base; arranging the wavelength-conversion member on the appliedmetal paste; joining the base and the wavelength-conversion member usinga sintered metal body obtained by heating the metal paste and sinteringthe metal powder, the sintered metal body having a porous structurecontaining voids; and impregnating the voids of the sintered metal bodywith resin by the resin impregnation method.

A wavelength-conversion module according to the present disclosureincludes: a base; a wavelength-conversion member provided on the base;and a joining member that joins the base and the wavelength-conversionmember, the joining member including: a sintered metal body having aporous structure containing voids; a resin including a first resinportion covering an outer surface of the sintered metal body and asecond resin portion with which the voids are impregnated; and particlesdispersed in the resin, in which a concentration of the particlesdispersed in the first resin portion is greater than a concentration ofthe particles dispersed in the second resin portion.

The resin impregnation method with the above-mentioned arrangement ofthe present disclosure is intended to provide a resin impregnationmethod that enables manufacture of a wavelength-conversion module withhigh reliability.

Further, the present disclosure enables providing thewavelength-conversion module with high reliability and a method ofmanufacturing the wavelength-conversion module.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments of the invention and many ofthe attendant advantages thereof will be readily obtained by referenceto the following detailed description when considered in connection withthe accompanying drawings.

FIG. 1 is a process flow of a resin impregnation method according to thepresent disclosure.

FIG. 2 is a top view of a wavelength-conversion module according to thepresent disclosure.

FIG. 3 is a sectional view of the wavelength-conversion module takenalong the line illustrated in FIG. 2 .

FIG. 4 is an enlarged sectional view illustrating a part of thesectional view of FIG. 3 .

FIG. 5 is a process flow of a method of manufacturing awavelength-conversion module according to the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, certain embodiments and examples for implementing thepresent disclosure will be described with reference to the drawings.Connection structures mentioned below are intended to embody thetechnical concepts of the present disclosure, and the present disclosureis not limited to the following unless otherwise specifically stated.

Throughout the respective drawings, members having the same function maybe denoted by the same sign. For the sake of convenience and ease ofexplanation or understanding of the main points, the description belowmay be separately given for each embodiment or example, but theconfigurations of different embodiments or examples could be partiallysubstituted or combined. In the following embodiments and examples, thedescription about matters common to the foregoing is omitted, and thusonly differences therebetween will be explained. In particular, similaractions and effects with similar configurations will not be mentionedsequentially for each embodiment or example. The size, positionalrelationship, etc., of members illustrated in the respective drawingsmay be exaggerated for clarity of the explanation.

Certain embodiments according to the present disclosure will bedescribed in detail below.

In the following description, the expression “excessive foaming” may bedefined as foaming that occurs when bubbles become large and break orthey are vigorously formed and break, on the surface of a resinmaterial.

First Embodiment

A resin impregnation method according to a first embodiment is a methodof impregnating voids of a sintered metal body having a porous structurewith resin, the method including, as illustrated in FIG. 1 :

-   -   (1) a resin material preparation S11 of preparing a resin        material that contains a defoamer containing hydrophilic or        hydrophobic particles;    -   (2) a defoaming S12 of defoaming the prepared resin material by        reducing its pressure;    -   (3) an applying S13 of applying the defoamed resin material onto        a surface of the sintered metal body;    -   (4) a resin impregnation S14 of impregnating the voids with the        resin material by reducing pressure of the sintered metal body        and the resin material applied to its surface so as to expel gas        from the voids; and    -   (5) a curing S15 of curing the resin material by heating.

Herein, the term “sintered metal body having a porous structure” as usedin the present disclosure refers to, for example, a sintered bodyobtained by firing a metal paste containing metal powder. The sinteredmetal body includes a metal part with a mesh structure in which aplurality of metal particles are continuously connected by fusingadjacent metal particles at least in part, and voids formed in spaces,other than the fused part, between the plurality of adjacent metalparticles. Therefore, in the sintered metal body having the porousstructure as used in the present disclosure, voids are present between awavelength-conversion member and a heat dissipation member in the caseof a wavelength-conversion module, for example.

The term “porous material” generally refers to a material having a largenumber of fine pores, such as microporous material, mesoporous material,and macroporous material. The sintered metal body in the presentdisclosure can contain voids of various sizes, depending on, forexample, the particle size distribution in the metal powder beforesintering. Furthermore, for example, when the sintered metal body in thepresent disclosure is used as a joining member to join two members,there is also a void in an area sandwiched between the two members,thereby making it possible to more effectively secure enough strength towithstand thermal stress.

The resin impregnation method according to the first embodiment will bedescribed in detail below.

(1) Resin Material Preparation S11

In the resin material preparation S11, a resin material that contains adefoamer containing hydrophilic or hydrophobic particles is prepared.

In this resin material preparation, first, a thermosetting epoxy resin,which is the main component of the resin material, is prepared. Althoughsilicone resin or the like can be used, epoxy resin is more preferredbecause it has a high gas barrier property and thereby can shield thesintered metal body from the outside air after impregnation.Thermosetting epoxy resins that do not contain halogens such as chlorineare preferred. Types of the epoxy resin include alicyclic epoxy resins,bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, hydrogenatedbisphenol A diglycidyl ether, hexahydrophthalic acid diglycidyl ester,and the like. To use the epoxy resin in the form of a liquid product,various epoxy reactive diluents may be added to the epoxy resin. Amongthem, alicyclic epoxy resins are preferred. Alicyclic epoxy resins haveexcellent filling properties because of their low viscosity, and thusare less likely to generate voids. The glass transition temperature ofthe alicyclic epoxy resin can be increased to 200° C. or higher, and canbe easily adjusted to an appropriate glass transition temperatureaccording to a required heatproof temperature.

The defoamer containing hydrophilic or hydrophobic particles isprepared, for example, by blending and dispersing the hydrophilic orhydrophobic particles (powder) in a medium such as silicone oil. Here,in addition to silicone oil, highly hydrophobic surfactants can be usedas the medium. However, the former, i.e., silicone oil is afoam-suppressing defoamer suitable for a non-water based resin, whilethe latter, i.e., the above-mentioned surfactants are foam-suppressingdefoamers suitable for a water-based resin. In this embodiment, siliconeoil is preferably used because most of the resin materials belong to thenon-water based category. As for the hydrophilic or hydrophobicparticles, hydrophilic silica, hydrophobic silica, and the like can beused. There are two types of defoamers: a foam-suppressing defoamerwhich can effectively suppress the generation of foam; and afoam-breaking defoamer which effectively breaks foam. Thefoam-suppressing properties are exerted when bubbles reach the surfaceof a liquid to inhibit the growth of the bubbles from the surface of theliquid to the outside. On the other hand, the foam-breaking propertiesare exerted after bubbles have grown and expanded from the surface of aliquid, making it easier for the bubbles to break. In the case of usingthe foam-breaking defoamer, bubbles themselves grow, and therefore itdoes not act to prevent the resin material from scattering or creepingup to the wavelength-conversion material.

The average particle size of the hydrophilic or hydrophobic particles tobe blended and dispersed in the medium is set appropriately, taking intoaccount the size of the void in an object to be impregnated and thesettling of the particles during storage. For example, the averageparticle size is 0.001 μm or more and 20 μm or less, preferably 0.01 μmor more and 10 μm or less, and more preferably 0.05 μm or more and 5 μmor less. The content of the hydrophilic or hydrophobic particles in themedium is, for example, 0.001 parts by weight or more and 10 parts byweight or less, preferably 0.01 parts by weight or more and 5 parts byweight or less, and more preferably 0.1 parts by weight or more and 3parts by weight or less, relative to 100 parts by weight of the medium.

The resin material is prepared by adding a predetermined amount ofdefoamer to the thermosetting epoxy resin prepared above and mixingthem. The content of the defoamer in the epoxy resin is, for example,0.001 parts by weight or more and 10 parts by weight or less, preferably0.005 parts by weight or more and 5 parts by weight or less, and morepreferably 0.01 parts by weight or more and 1 part by weight or less,relative to 100 parts by weight of the epoxy resin. The resin materialcan contain, for example, a wet conditioner or a viscosity adjuster.

The resin material can also contain a filler in order to preventcracking during thermal shock. For example, a filler such as silica oralumina can be used.

(2) Defoaming S12

In the defoaming S12, the prepared resin material is defoamed by beingheld under a reduced pressure before application.

For example, in the case of placing the resin material in a syringe andapplying it in the applying S13 mentioned below, the whole syringefilled with the resin material is placed in a vacuum defoaming apparatusand then defoamed for each syringe before the application. Reducing thepressure of the resin material to defoam it in this way enablesefficient defoaming of bubbles which are contained in the resin materialduring the preparation of the resin material or filling of the syringeand which are very small and cannot float up to the surface of the resindue to their low buoyancy. For example, the degree of vacuum during thisdefoaming is set in the range from 10⁻³ Pa to 10³ Pa, preferably from10⁻² Pa to 10² Pa, and more preferably from 10⁻¹ Pa to 10 Pa.

Since the resin material of the first embodiment contains the defoamer,bubbles can be prevented from becoming large before defoaming even whenthe pressure of the resin material is reduced in the defoaming S12.Thus, for example, the resin material can be prevented from beingspilled from the syringe.

(3) Applying S13

In the applying S13, the defoamed resin material is applied to thesurface of the sintered metal body.

The amount of resin to be applied is set greater than or equal to anamount of resin with which all the voids of the sintered metal body arefilled. Specifically, for example, the entire volume of voids in thesintered metal body is determined based on the sintered concentration ofthe sintered metal body and the whole volume of sintered metal body, andthen the amount of resin to be applied is set in such a manner as to begreater than or equal to the determined entire volume of voids. Here,the resin material to be applied preferably has a low viscosity inconsideration of filling the voids of the sintered metal body therewith,but lowering the viscosity of the resin material has the followingissues. For example, in the case of using the sintered metal body as ajoining member that joins two members, the surface of the sintered metalbody with which the resin is to be applied is usually not horizontal butsloped. In such a case, the applied resin material may spreadhorizontally and reach areas where the resin material should not beapplied, such as wire pads. Therefore, it is preferable to devise meansfor suppressing the horizontal spread of the applied resin material. Themeans for suppressing the horizontal spread of the resin material willbe described in the embodiments below.

(4) Resin Impregnation S14

In the resin impregnation S14, the voids are impregnated with the resinmaterial by reducing the pressure of the sintered metal body and theresin material applied to its surface so as to expel gas from the voids.The degree of vacuum during the impregnation is set appropriately insuch a manner as to cause all the voids to be impregnated with the resinmaterial while suppressing excessive foaming, based on the volume ratioof the voids in the sintered metal body and the size of the void. Forexample, the degree of vacuum is set in the range from 10⁻³ Pa to 10³Pa, preferably from 10⁻² Pa to 10² Pa, and more preferably from 10⁻¹ Pato 10 Pa. Since air remaining under a chip has a certain, large volumein the applying S13 of the resin, it floats up to the surface of theresin by its own buoyancy, and is released to some extent from under thechip even at normal pressure, unlike the defoaming S12. However, thisair is not completely released and therefore it is necessary to reducethe pressure of the resin. In the resin impregnation method of the firstembodiment, the resin material contains the defoamer in whichhydrophilic or hydrophobic particles are blended as mentioned above.Thus, in the resin impregnation S14, gas in the voids is expelled in theform of small bubbles to deform the resin material without allowing thebubbles to grow into large bubbles on the surface of the resin materialeven when the pressure of the resin material is reduced after applyingthe resin material. This enables removal of the gas inside the voidswhile suppressing the excessive foaming, thereby suppressing unnecessaryscattering or spread of the resin material. The bubbles contained in theresin material itself are removed by the reducing its pressure beforethe application. Consequently, the foaming of the resin material due tothe bubbles contained in the resin material itself can be suppressed.The hydrophilic or hydrophobic particles (powder) contained in thedefoamer are less likely to penetrate into the centers of the voids ofthe sintered metal body because they are particles, and they do not needto penetrate into the centers. In other words, even if the particlesstay near the surface of the sintered metal body with the resin materialapplied thereto, the foam-suppressing or breaking function of theparticles is remained near the surface of the sintered metal body,whereby excessive foaming of the resin material is suppressed.

(5) Curing S15

In the curing S15, the resin material with which the voids areimpregnated is cured by heating.

The resin impregnation method according to the first embodiment with theabove-mentioned arrangement includes the defoaming S12 of defoaming theresin material by reducing its pressure before the application, so thatthe excessive foaming of the resin material due to bubbles contained inthe resin material itself can be suppressed even when the pressure ofthe resin material is also reduced in the resin impregnation S14 afterthe application.

Since the resin material contains the defoamer in which hydrophilic orhydrophobic particles are blended, gas in the voids is expelled in theform of small bubbles to deform the resin material without allowing thebubble to grow into large bubbles in the resin material even when thepressure of the resin material is reduced after applying the resinmaterial. This makes it possible to suppress excessive foaming of theresin material.

Therefore, according to the resin impregnation method of the firstembodiment, the voids of the sintered metal body are allowed to beimpregnated with the resin, while suppressing the unnecessary scatteringand spread of the applied resin material.

Second Embodiment

A second embodiment relates to a wavelength-conversion module fabricatedby a manufacturing method that includes the resin impregnation method ofthe first embodiment. The wavelength-conversion module converts thewavelength of light from a light-emitting element such as asemiconductor laser to another wavelength using a phosphor and emits thelight with the converted wavelength.

The wavelength-conversion module of the second embodiment will bedescribed in detail below with reference to FIGS. 2 to 4 . FIG. 2 is atop view of the wavelength-conversion module according to the presentdisclosure. FIG. 3 is a sectional view of the wavelength-conversionmodule taken along the line illustrated in FIG. 2 . FIG. 4 is anenlarged sectional view illustrating a part of the sectional view ofFIG. 3 .

The wavelength-conversion module 100 of the second embodiment includes abase 30, a wavelength-conversion member 10 provided on the base 30, anda joining member 20 that joins the base 30 and the wavelength-conversionmember 10.

In the second embodiment, the base 30 includes a base portion 31 havinga concave portion 31 a, a first metal layer 32 provided on an uppersurface of the base portion 31 including an inner surface of the concaveportion 31 a, and a second metal layer 33 provided on the first metallayer 32.

The wavelength-conversion member 10 includes a phosphor plate 11, ananti-reflection layer 12 provided on an upper surface of the phosphorplate 11, and a joining layer 13 provided on a lower surface of thephosphor plate 11.

The phosphor plate 11 can be composed of, for example, a YAG plate madeof a sintered body of yttrium aluminum garnet or a LAG plate made of asintered body of lutetium aluminum garnet. The phosphor plate 11 ispreferably composed of a YAG plate.

The anti-reflection layer 12 can be composed of a metal oxide such asSiO₂, Nb₂O₅, or TiO₂, or a nitride such as SiN, GaN, or AlN. Theanti-reflection layer 12 is preferably composed of SiO₂.

The joining layer 13 includes a light-shielding layer 13 a provided onthe lower surface of the phosphor plate 11 and a metal joining layer 13b provided on a lower surface of the light-shielding layer 13 a. Thelight-shielding layer 13 a can be composed of, for example, an Al₂O₃film, a SiO₂ film, a Nb₂O₅ film, or a TiO₂ film. The light-shieldinglayer 13 a is preferably composed of an Al₂O₃ film. The metal joininglayer 13 b can be composed of, for example, an Ag film, a lamination of,a Ni film and an Ag film, a lamination of an Ag film and an Au film, alamination of an Al film and an Ag film, an Au film, a lamination of anAl film and an Au film, and a lamination having an arbitrary metal layeras a barrier layer for adhesion and heating sandwiched between the filmsof the above-mentioned lamination. The joining layer 13 b is preferablycomposed of an Ag film.

In the second embodiment, the base 30 and the wavelength-conversionmember 10 are joined via the joining member 20. The joining member 20includes a sintered metal body 21 having a porous structure containingvoids, a resin 50, and particles 53 dispersed in the resin 50. The resin50 includes a first resin portion 51 covering an outer surface of thesintered metal body 21 and a second resin portion 52 with which thevoids are impregnated. Here, the sintered metal body preferably containssilver or copper, and more preferably contains silver. Both the firstresin portion 51 and the second resin portion 52 can contain theparticles 53. The second resin portion 52 hardly contains particles 53inside the sintered metal body 21, and the particles 53 are located nearthe outer surface of the sintered metal body 21. In other words, in thesecond resin portion 52, the concentration of the particles 53 containedin a part of the second resin portion 52 located near the outer surfaceof the sintered metal body 21 is greater than the concentration of theparticles 53 contained in a part of the second resin portion 52 locatedinside the sintered metal body 21. Further, the concentration of theparticles 53 dispersed in the first resin portion 51 is greater than theconcentration of the particles 53 dispersed in the second resin portion52 inside the sintered metal body 21.

The dispersed particles 53 act on the surfaces of bubbles in the resinmaterial, which is used to form the resin 50 during the manufacture,when the bubbles reach the surface of the liquid resin material, therebydestabilizing the surfaces of the bubbles by disrupting the arrangementof the resin material. In this way, the particles 53 have the functionof inhibiting the growth of the bubbles from the liquid surface. Asmentioned below, the foam-suppressing function of the particles 53 inthe resin member only needs to be remained within the first resinportion 51, and thus the second resin portion 52 may not substantiallycontain the particles 53.

In the joining member 20, the sintered metal body 21 can have a filletthat spreads toward the base 30, and the fillet can cover at least aportion of the side surfaces, i.e., the lateral surfaces of thewavelength-conversion member 10. When the sintered metal body 21contains the fillet covering a portion of the side surfaces of thewavelength-conversion member 10, the surface of the fillet is coveredwith the first resin portion 51. The thickness of the first resinportion 51 on the fillet surface is preferably 1 μm or more. If thethickness of the first resin portion 51 on the fillet surface issufficient, the sintered metal body is shielded from the outside air,and thus can be protected from sulfurization and oxidation. Thethickness of the first resin portion 51 on the fillet surface can bechecked with a cross-sectional SEM, for example.

The sintered metal body 21 may contain spacer particles to make thethickness of the joining member 20 greater than or equal to a certainthickness, which allows the thickness of the sintered metal body 21 orjoining member 20 between the base and the wavelength-conversion memberto be the same or thicker than the particle size of the spacerparticles. The spacer particles can be composed of zirconia particles,glass particles, silica particles, or alumina particles. The spacerparticles are preferably composed of zirconia particles. The particlesize of the spacer particles can be set appropriately in considerationof the spacing which is to be secured between the base and thewavelength-conversion material. The particle size of the spacerparticles is set in the range of 20 μm or more and 500 μm or less,preferably in the range of 50 μm or more and 300 μm or less, and morepreferably in the range of 100 μm or more and 200 μm or less.

The wavelength-conversion module 100 of the second embodiment with theabove-mentioned configuration can be provided by the manufacturingmethod including the resin impregnation method of the first embodimentas mentioned in detail below so as to have high wavelength-conversionefficiency without any contamination of the upper surface (emissionsurface) of the wavelength-conversion member 10 due to the resinmaterial in forming the resin 50.

In addition, the occurrence of blooming and bleeding on the surface ofthe resin 50 can be prevented by manufacturing the wavelength-conversionmodule 100 using the manufacturing method including the resinimpregnation method of the first embodiment. This makes it possible toprovide the wavelength-conversion module with highly elaborate designwhen viewing the wavelength-conversion module from the light-emittingsurface side.

While wavelength-conversion module 100 of the second embodiment with theabove-mentioned configuration has been described using an example of thebase 30 which has a package structure with an annular convex portion forforming the concave portion 31 a, the wavelength-conversion module 100may be configured using a plate-shaped substrate as the base.

When a plate-shaped substrate is used as the base, instead of theannular convex portion for forming the concave portion 31 a, it ispreferable to form an annular convex or concave part with a lowerprofile structure than the annular convex portion for forming theconcave portion 31 a, on the upper surface of the base (the substrate).The annular convex or concave part having the lower profile structurecan be at a lower height than the thickness of the sintered metal body.The annular convex or concave part can stop the resin 50 from spreadingdue to surface tension when it is formed.

(Method of Manufacturing Wavelength-Conversion Module 100)

The manufacturing method of the wavelength-conversion module 100includes a first applying S21, an arranging S22, a joining S23, and animpregnation S24 including the resin impregnation method of the firstembodiment, as illustrated in FIG. 5 .

In the first applying, a metal paste containing metal powder isprepared, and the metal paste is applied onto the base.

In the arranging, the wavelength-conversion member is arranged on theapplied metal paste.

In the joining, the metal paste is heated to sinter the metal powder,thereby joining the base and the wavelength-conversion member using thesintered metal body having a porous structure containing voids.

In the impregnation, the voids of the sintered metal body areimpregnated with resin by using the resin impregnation method of thefirst embodiment.

Hereinafter, each process will be described in detail.

In the manufacturing method of the wavelength-conversion module 100, theprocesses from the first applying to the impregnation are carried outafter preparing the wavelength-conversion member 10 and the base 30mentioned above.

1. First Applying S21

Here, the metal paste containing the metal powder is first prepared.

(1) Preparation of Metal Paste

In the description below, the case of using silver particles as themetal particles will be described below, and the metal paste will bereferred to as a silver paste.

(1-1) Preparation of Silver Particles

The shape of the silver particles to be prepared is not limitedparticularly to, but may be, for example, a substantially sphericalshape or a flake shape. The expression that the silver particle has a“substantially spherical shape” as used herein means that the aspectratio (a/b), which is defined as the ratio of the major axis a to theminor axis b, of the silver particle is less than or equal to two. Theexpression that the silver particle has a “flake shape” as used hereinmeans that the aspect ratio of the silver particle is greater than 2.The major axis a and the minor axis b of the silver particle can bemeasured by image analysis with the SEM.

The silver particles to be prepared have an average particle size of,for example, 0.3 μm or more, preferably 0.5 μm or more, more preferably1 μm or more, and still more preferably 2 μm or more. The silverparticles preferably have an average particle size of, for example, 10μm or less, and more preferably 5 μm or less. When the average particlesize of the silver particle is 0.5 μm or more, and more preferably 1 μmor more, the silver particles do not aggregate without forming aprotective film such as a capping agent on the surfaces of the silverparticles, thus eliminating the need for thermal decomposition of theprotective film and enabling sintering at a low temperature. The largerparticle size of silver particles improves the fluidity of the silverpaste. Thus, if silver pastes have the same fluidity (workability), thesilver paste containing silver particles with sizes in this specifiedrange could contain more silver particles. When the average particlesize is 10 μm or less, and more preferably 5 μm or less, the meltingpoint depression phenomenon occurs due to the larger specific surfacearea of the silver particles, and as a result, the sintering temperaturecan be lowered. The particle size of silver particles can be measured bya laser diffraction method. The term “average particle size” as usedherein means the volume-based median diameter (which is a value obtainedwhen a cumulative volume frequency determined from the particle sizedistribution is 50%) measured by the laser diffraction method.

As the silver particles to be prepared, preferably, the content ofsilver particles with a particle size of less than 0.3 μm in the silverpaste is 5% by mass or less. More preferably, the content of silverparticles with a particle size of 0.5 μm or less is 15% by mass or less.Silver particles tend to be sintered at a lower temperature as theparticle size decreases. In particular, nano-sized silver particles aresintered at a lower temperature than micro-sized silver particles. Thus,if the content of nano-sized silver particles in the silver paste islarge, sintering may start at a low temperature, and fusion may occurwithout sufficient contact between the silver particles.

The silver particles to be prepared may have a small amount of silveroxide films or silver sulfide films present on their surfaces. Sincesilver is a noble metal, the silver particles themselves are less likelyto be oxidized and are very stable. However, when viewed in a nano-sizedregion, they tend to adsorb sulfur, oxygen, etc., from the air or thelike, thereby forming a thin film on the surface of the silver particle.The thickness of the oxide film or sulfide film of silver particles ispreferably 50 nm or less and more preferably 10 nm or less.

1-2. Mixing of Silver Particles and Organic Solvent

Here, the prepared silver particles are mixed with an organic solvent asa dispersion medium.

Further, the silver paste may contain resin or the like.

The content of silver particles when mixed is preferably 70% by mass ormore, and more preferably 85% by mass or more. The resin that can bemixed with the silver paste is one that decomposes upon heating duringfiring as mentioned below, and does not remain in the formed joiningbody. The resin may be, for example, polystyrene (PS) or polymethylmethacrylate (PMMA). Mixing the silver particles with an organicsolvent, which is the dispersion medium, makes it easier to apply thesilver paste with the desired thickness onto the surface of the base.The organic solvent used here can be one type of organic solvent or amixture of two or more types of organic solvents. For example, a mixtureof a diol and an ether can be used. The boiling point of the organicsolvent is preferably in the range of 150° C. or higher and 250° C. orlower. The organic solvent having a boiling point of 150° C. or highercan prevent contamination of the silver particles with the atmosphereand chip dropout that would be caused due to the drying of the silverpaste before the heating. The organic solvent having a boiling point of250° C. or lower can increase the volatilization rate during the heatingand accelerate sintering.

In addition to the silver particles and the dispersion medium, additivessuch as a dispersant, a surfactant, a viscosity adjuster, and a dilutingsolvent, as well as spacer particles may be mixed with the silver paste.As the content of the additives in the silver paste, the total amount ofadditives in the silver paste may be 5% by mass or less, for example, inthe range of 0.5% by mass or more and 3% by mass or less. In particular,the addition of the spacer particles is desirable because it enablesreproducible control of the thickness of the metal paste, which in turnallows for stable impregnation of the resin.

Although the above description has been given on an example of thesilver paste composed of the silver particles, this embodiment is notlimited to the silver paste, but can also use a metal paste containingmetal particles other than silver particles, such as copper particles.

(2) Application of the Prepared Metal Paste onto Base

Here, the metal paste is applied onto the base 30.

Specifically, the prepared metal paste is applied onto the bottomsurface of the concave portion 31 a.

As the application method of the metal paste, appropriate known methodscan be adopted, and examples thereof include screen printing, offsetprinting, inkjet printing, flexographic printing, dispenser printing,gravure printing, stamping, dispensing, squeegee printing, silk screenprinting, spraying, brushing, coating, and the like. The appropriatethickness of the applied metal paste can be set according to theapplications or the like. For example, it can be 1 μm or more and 1000μm or less, preferably 5 μm or more and 800 μm or less, and morepreferably 10 μm or more and 500 μm or less.

2. Arranging S22

The wavelength-conversion member 10 is placed on top of the metal pasteapplied onto the bottom surface of the concave portion 31 a. Forexample, the wavelength-conversion member 10 is placed from above themetal paste and pressed against the metal paste such that the metalpaste between the bottom surface of the concave portion 31 a and thewavelength-conversion member 10 reaches a predetermined thickness,preferably such that the metal paste creeps up on parts of the sidesurfaces of the wavelength-conversion member 10.

3. Joining S23

In the joining, by heating the metal paste, the organic solvent isvolatilized and the metal particles are fused, thereby sintering themetal powder. Consequently, the base 30 and the wavelength-conversionmember 10 are joined by the sintered metal body having a porousstructure containing the voids.

The heating and firing here can also be performed by heating in areducing atmosphere, followed by firing in an oxidizing atmosphere, asappropriate.

(1) Heating Temperature

(1-1) Heating in Reducing Atmosphere

Heating in a reducing atmosphere is optional and thus performed asappropriate, as mentioned above. The heating in the reducing atmosphereis performed to remove a small amount of oxide films or the like presenton the surfaces of the metal particles, through the reduction.Consequently, metal atoms are exposed on the surfaces of the metalparticles, thereby promoting the surface diffusion of metal atoms on thesurfaces of the metal particles. Therefore, the sintering of metalparticles can be promoted at a low temperature by the subsequent heatingin an oxidizing atmosphere.

The heating in the reducing atmosphere and the heating in the oxidizingatmosphere, which will be described later, may be performed in separatedevices, but they are preferably performed in the same device. Thus, theheating in the reducing atmosphere and the heating in the oxidizingatmosphere can be continuously performed in the same device. Thereducing atmosphere is preferably a formic-acid containing atmosphere ora hydrogen containing atmosphere. For example, it is preferably amixture of a formic acid or hydrogen with an inert gas such as nitrogen.The reducing atmosphere more preferably contains a formic acid. Forexample, it is preferably a mixture of a formic acid with an inert gassuch as nitrogen.

The heating in the reducing atmosphere is performed, for example, at atemperature of lower than 300° C., preferably 280° C. or lower, morepreferably 260° C. or lower, and still more preferably 200° C. or lower.The heating in the reducing atmosphere is preferably performed, forexample, at a temperature of 150° C. or higher, more preferably 160° C.or higher, and still more preferably 180° C. When the heatingtemperature is 150° C. or higher, more preferably 160° C. or higher, andstill more preferably 180° C. or higher, the reaction rate of thereduction reaction of the oxide film present on the silver particlesurface can be accelerated. The pressure at which the heating isperformed in the reducing atmosphere is not particularly limited, butmay be an atmospheric pressure, for example.

(1-2) Firing in Oxidizing Atmosphere

Here, by heating and firing in an oxidizing atmosphere, the metalparticles are fused together to form the sintered metal body. Theoxidizing atmosphere is preferably an oxygen-containing atmosphere, andmore preferably an atmospheric atmosphere. When the oxidizing atmosphereis an oxygen-containing atmosphere, the oxygen concentration in theatmosphere is preferably in the range of 2% by volume or more and 21% byvolume or less. The higher the oxygen concentration in the atmosphere,the more the surface diffusion of metal atoms on the surfaces of themetal particles is promoted, and the more easily the metal particlestend to be fused together. When the oxygen concentration is 2% by volumeor higher, the metal particles can be fused together at a lower heatingtemperature. When the oxygen concentration is 21% by volume or lower, apressurizing mechanism is not required in a heating device, thusenabling the reduction in the process cost.

(2) Firing Temperature

The firing temperature in the oxidizing atmosphere is, for example, 300°C. or lower, preferably 280° C. or lower, more preferably 260° C. orlower, and still more preferably 200° C. or lower. By heating in thereducing atmosphere before the firing in the oxidizing atmosphere, thefiring can be performed at a lower temperature.

The firing in the oxidizing atmosphere is preferably performed, forexample, at a temperature of 150° C. or higher, and more preferably 160°C. or higher. By setting the firing temperature to 150° C. or higher andmore preferably 160° C. or higher, the sintered metal body with lowelectrical resistivity and good thermal conductivity properties can beformed.

The firing in the oxidizing atmosphere may be performed under apressurized condition, for example, under an atmospheric pressure.

4. Impregnation S24

In the impregnation, the voids of the sintered metal body areimpregnated with resin according to the resin impregnation method of thefirst embodiment.

Here, the resin material that contains the defoamer containing thehydrophilic or hydrophobic particles is prepared (resin materialpreparation S11).

Before the prepared resin material is applied, it was defoamed byreducing its pressure (defoaming S12). For example, the syringe isfilled with the resin material, placed itself in a vacuum defoamingapparatus, and then defoamed for each syringe before the application.

Next, the defoamed resin material is applied onto a surface of thesintered metal body (applying S13). Here, the resin material obtainedafter the defoaming is applied, for example, by the syringe onto theinside of the outer concave portion 31 a of the wavelength-conversionmember 10, i.e., in a region between the side surface of the concaveportion 31 a and the surface of the fillet.

Next, gas in the voids is expelled by reducing the pressure of the resinmaterial applied onto the surface of the sintered metal body (thesurface of the fillet), thereby impregnating the voids with the resinmaterial (resin impregnation S14).

Finally, the resin material with which the voids are impregnated iscured by heating (curing S15).

In the way mentioned above, the wavelength-conversion module of thesecond embodiment is fabricated.

According to the above-mentioned manufacturing method of thewavelength-conversion module, the resin portion 50 can be formed byimpregnating the voids of the sintered metal body 21 with the resinmaterial, while suppressing excessive foaming through the pressurereduction in the resin impregnation without allowing the resin materialto creep up on the light-emitting surface of the wavelength-conversionmember 10.

Therefore, the wavelength-conversion module fabricated by themanufacturing method can enhance its thermal stress durability bycausing the resin to be included in the voids of the sintered metal body21, and can suppress the reduction in light extraction efficiency due tothe absence of contamination of the light-emitting surface with theresin material, resulting in high luminous efficiency.

EXAMPLES Example 1

In Example 1, the wavelength-conversion module 100 illustrated in FIG. 2was fabricated in the following manner. Preparation of Base 30

The base 30 was prepared to include the base portion 31 made of copperand having the concave portion 31 a, the base portion being providedwith a Ni plating layer of 2 μm in thickness as the first metal layer32, and an Au plating layer of 0.05 μm in thickness as the second metallayer 33.

(2) Fabrication of Wavelength-conversion Member 10

In this example, an integrally sintered alumina-YAG plate of 0.2 mm inthickness was prepared as the phosphor plate 11. Here, the prepared YAGplate contains Y₂O₃, Al₂O₃, and CeO₂.

Then, an Al₂O₃ film of 1 μm in thickness was deposited on a lowersurface of the YAG plate by sputtering, and an Ag film of 0.5 μm inthickness was deposited on top of the Al₂O₃ film by sputtering.

In addition, a SiO₂ film of 0.11 μm in thickness was deposited on anupper surface of the YAG plate by sputtering. Consequently, awavelength-conversion member plate in which a plurality ofwavelength-conversion members 10 were integrated was fabricated.

Then, the wavelength-conversion member plate was singulated by dicinginto wavelength-conversion members 10, each having dimensions of 5.5mm×5.5 mm×0.2 mm.

(3) Preparation and Application of Metal Paste and Arrangement ofWavelength-conversion Member

A silver paste was prepared as the metal paste to join thewavelength-conversion member 10 to the base 30. To prepare the silverpaste, first, 2-ethyl-1,3-hexanediol (0.852 g), diethylene glycolmonobutyl ether (0.213 g), which were organic solvents, and an anionicliquid surfactant (manufactured by Sanyo Chemical Industries, Ltd.,trade name “Viewlite LCA-H”, laureth-5-carboxylic acid, liquid at 25°C., 0.150 g) were mixed and stirred with a rotating-revolving mixer(trade name “Awatori Rentaro AR-250” manufactured by Thinky Corporation)for one minute, followed by defoaming for one cycle of 15 seconds whilestirring, thereby producing a solvent mixture.

Next, flake-shaped silver particles (manufactured by Fukuda Metal Foil &Powder Co., Ltd., product name “AgC-239”, flake-shaped, average particlesize (median diameter) of 2.5 μm, specific surface area of 0.7 m²/g, thecontent of particles with a particle size of less than 0.3 μm being 2%by mass, the content of particles with a particle size of 0.5 μm or lessbeing 6% by mass, 13.776 g) as well as zirconia particles with aparticle size of 100 μm (manufactured by NIKKATO CORPORATION, trade name“YTZ Ball”, 0.009 g) as spacer particles were weighed and added to theabove-mentioned solvent mixture. The resulting mixture was stirred forone minute and defoamed for 15 seconds, which were set as one cycle,with the rotating-revolving mixer (trade name: “Awatori Rentaro AR-250”,manufactured by Thinky Corporation) to obtain a silver paste (notcontaining any resin).

Next, the prepared silver paste was applied onto the bottom surface ofthe concave portion 31 a of the base 30.

Subsequently, the wavelength-conversion member 10 was arranged on theapplied silver paste using a die bonder.

(4) Joining

The base 30 with the wavelength-conversion member arranged therein wasplaced in an oven and fired, so that the silver powder contained in thefired silver paste was sintered in the atmosphere to join the base 30and the wavelength-conversion member 10.

The firing temperature was raised to 200° C. at a temperature-increaserate of 0.24° C./min and held at 200° C. for one hour to sinter thesilver powder.

(5) Preparation of Impregnation Resin

First, as an impregnating resin, foam-suppressing silicone oil compoundtype (containing silica particles) defoamer KS-66 (manufactured byShin-Etsu Chemical Co. Ltd., 0.005 g, 0.1%) was added to epoxy resinCELVENUS W221 (manufactured by Daicel Corporation, two-component type,thermosetting type, 5.000 g) to thereby fabricate a resin material.

(6) Defoaming Before Application of Resin Material

An applicating syringe was filled with the prepared resin material,which was then defoamed by the vacuum defoaming apparatus for eachsyringe.

The defoaming was performed using an oil-sealed rotary vacuum pump(manufactured by ULVAC, Inc., GLD-136C) with an ultimate vacuum of 0.67Pa for 30 seconds as defoaming conditions.

(7) Application of Resin Material

The resin material was applied onto the inside of the concave portion 31a with an air dispenser using the syringe in which the defoamed resinmaterial was placed. Specifically, by filling a space between the innercircumferential wall of the concave portion 31 a and an outercircumferential side surface of the wavelength-conversion member withresin material, the resin material was applied onto the surface of thefillet formed on the periphery of the wavelength-conversion member ofthe sintered silver body.

(8) Impregnation with Resin Material

After applying the resin material, the base 30 with thewavelength-conversion member 10 joined thereto was subjected to pressurereduction in the vacuum defoaming apparatus to expel air from the voidsof the sintered silver body, causing the voids to be impregnated withthe resin material. The pressure reduction was performed using theoil-sealed rotary vacuum pump (manufactured by ULVAC, Inc., GLD-136C)with an ultimate vacuum of 0.67 Pa for 10 minutes as pressure reducingconditions.

(9) Resin Curing

The whole base 30 to which the wavelength-conversion member 10 wasjoined was heated in the atmosphere using an oven to cure the resinmaterial. Curing conditions were set to 150° C. and one hour.

The wavelength-conversion module of Example 1 fabricated as mentionedabove enabled impregnation of all the voids of the joining member withthe resin, and also enabled efficient wavelength conversion withoutcontamination of the upper surface (the light-emitting surface) of thewavelength-conversion member due to the resin material. In this way, thewavelength-conversion module with higher reliability can be produced.

Comparative Example 1

A wavelength-conversion module of Comparative Example 1 was fabricatedin the same manner as in Example 1, except that an impregnated resinwhich did not contain a defoamer was used.

In the wavelength-conversion module of Comparative Example 1, the uppersurface (the light-emitting surface) of the wavelength-conversion memberwas contaminated with the resin material, and the wavelength-conversionefficiency was inferior to that of the wavelength conversion module ofExample 1.

The resin impregnation method according to the present embodiments canbe used to fix semiconductor elements or sub-mount substrates. Thewavelength-conversion module and its manufacturing method can be used inautomobile headlights, lighting fixtures, projectors, and otherapplications.

What is claimed is:
 1. A method of impregnating with resin voids of asintered metal body having a porous structure, the method comprising:preparing a resin material that contains a defoamer containinghydrophilic or hydrophobic particles; defoaming the prepared resinmaterial by reducing pressure of the resin material; applying thedefoamed resin material onto a surface of the sintered metal body;impregnating the voids with the resin material by reducing pressure ofthe sintered metal body and the resin material applied to the surface ofthe sintered metal body so as to expel gas from the voids; and curingthe resin material by heating, wherein, after the curing the resinmaterial, the defoamer has not penetrated into the center of the voidsof the sintered metal body and has remained near the surface of thesintered metal.
 2. The method of impregnating resin according to claim1, wherein the hydrophilic or hydrophobic particles are silicaparticles.
 3. The method of impregnating resin according to claim 1,wherein the resin material is epoxy resin.
 4. The method of impregnatingresin according to claim 1, wherein the voids of the sintered metal bodyhaving porous structure are connected in a mesh shape.
 5. The method ofimpregnating resin according to claim 1, wherein the voids of thesintered metal body having porous structure include voids with adiameter of 2 μm or less in the lateral direction.
 6. A method ofmanufacturing a wavelength-conversion module comprising joining awavelength-conversion member onto a base using a joining member, themethod comprising: preparing a metal paste containing metal powder andapplying the metal paste onto the base; arranging thewavelength-conversion member on the applied metal paste; joining thebase and the wavelength-conversion member using a sintered metal bodyobtained by heating the metal paste and sintering the metal powder, thesintered metal body having a porous structure containing voids; andimpregnating the voids of the sintered metal body with resin by a resinimpregnation method comprising: preparing a resin material that containsa defoamer containing hydrophilic or hydrophobic particles; defoamingthe prepared resin material by reducing pressure of the resin material;applying the defoamed resin material onto a surface of the sinteredmetal body; impregnating the voids with the resin material by reducingpressure of the sintered metal body and the resin material applied tothe surface of the sintered metal body so as to expel gas from thevoids; and curing the resin material by heating.
 7. The method ofmanufacturing a wavelength-conversion module according to claim 6,wherein the metal powder is a silver powder having a median diameter of0.3 μm or more and 5 μm or less.
 8. The method of manufacturing awavelength-conversion module according to claim 6, wherein the metalpaste containing the silver powder is heated to sinter the silver powderat a temperature of 160° C. or higher and 300° C. or lower when joiningthe base and the wavelength-conversion member.
 9. The method ofmanufacturing a wavelength-conversion module according to claim 6,further comprising, prior to arranging the wavelength-conversion member,preparing the wavelength-conversion member which includes a phosphorplate with a lower surface and an upper surface, an Al₂O₃ film providedon the lower surface of the phosphor plate, and an Ag film provided on alower surface of the Al₂O₃ film, wherein the wavelength-conversionmember is arranged so that the Ag film faces the base when arranging thewavelength-conversion member.
 10. The method of manufacturing awavelength-conversion module according to claim 6, further comprising,prior to the arranging the wavelength-conversion member, preparing thewavelength-conversion member which includes a phosphor plate with alower surface and an upper surface and a SiO₂ film provided on the uppersurface of the phosphor plate, wherein the wavelength-conversion memberis arranged so that the lower surface of the wavelength-conversionmember faces the base when arranging the wavelength-conversion member.11. The method of manufacturing a wavelength-conversion module accordingto claim 6, wherein, prior to applying the metal paste, an Au plating isprovided on the surface of a base portion of the base, and wherein thewavelength-conversion member is arranged such that the Au plating facesthe lower surface of the wavelength-conversion member when arranging thewavelength-conversion member.
 12. The method of manufacturing awavelength-conversion module according to claim 6, wherein the uppersurface of the base comprises an annular concave portion or convexportion surrounding an area for arranging the wavelength-conversionmember, the annular concave portion or convex portion preventing theapplied resin material from spreading outside the area, and prior tojoining the base and the wavelength conversion member, the defoamedresin material is applied inside the annular concave portion or convexportion when applying the defoamed resin material.
 13. The method ofmanufacturing a wavelength-conversion module according to claim 6,wherein, the metal paste further contains spacer particles and thethickness of the sintered metal body between the base and thewavelength-conversion member is set to the same or thicker than theparticle size of the spacer particles.